It could be any of those 3 things - spotting
before your period, a UTI, or a miscarriage. Something else that comes to mind is kidney stones
. Are you having any other symptoms? Symptoms of ANYTHING, I mean... body aches, rash, unexplained fatigue, pus, dark urine, etc. etc. It's tough to diagnose without a bit more info. Regardless, I would recommend making an appointment to see your doctor.